7.

Functional description

 

 

7.1 General operation

 

The LM75B uses the on-chip band gap sensor to measure the device temperature with

the resolution of 0.125

C and stores the 11-bit two’s complement digital data, resulted

from 11-bit A-to-D conversion, into the device Temp register. This Temp register can be

read at any time by a controller on the I2C-bus. Reading temperature data does not affect

the conversion in progress during the read operation.

 

The device can be set to operate in either mode: normal or shutdown. In normal operation

mode, the temp-to-digital conversion is executed every 100 ms and the Temp register is

updated at the end of each conversion. During each ‘conversion period’ (Tconv) of about

100 ms the device takes only about 10 ms, called ‘temperature conversion time’ (tconv(T)),

to complete a temperature-to-data conversion and then becomes idle for the time

remaining in the period. This feature is implemented to significantly reduce the device

power dissipation. In shutdown mode, the device becomes idle, data conversion is

disabled and the Temp register holds the latest result; however, the device I2C-bus

interface is still active and register write/read operation can be performed. The device

operation mode is controllable by programming bit B0 of the configuration register. The

temperature conversion is initiated when the device is powered-up or put back into normal

mode from shutdown.

 

In addition, at the end of each conversion in normal mode, the temperature data (or Temp)

in the Temp register is automatically compared with the over temperature shutdown

threshold data (or Tth(ots)) stored in the Tos register, and the hysteresis data (or Thys)

stored in the Thyst register, in order to set the state of the device OS output accordingly.

The device Tos and Thyst registers are write/read capable, and both operate with 9-bit

two’s complement digital data. To match with this 9-bit operation, the Temp register uses

only the 9 MSB bits of its 11-bit data for the comparison.

 

The way that the OS output responds to the comparison operation depends upon the OS

operation mode selected by configuration bit B1, and the user-defined fault queue defined

by configuration bits B3 and B4.

 

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4

友台半导体有限公司

 

UMW

LM75B